Intravenous fluid delivery systems often incorporate a device for determining the actual flow of the liquid to the patient. The detector may operate by determining when each drop has fallen in a drip chamber.
To accomplish this objective, the system passes a beam of electromagnetic radiation through the drip chamber itself. The passage of a drop should, under varying conditions, interrupt the light beam which the detector may then discover. It utilizes this information to determine that a drop indeed has fallen.
The difficulty encountered by this type of flow detector centers upon the necessity of detecting a drop falling anywhere in the drip chamber itself. The use of a beam emanating from a single emitter and traveling to a single receiver has not provided coverage for the entire interior of the drip chamber with substantially uniform radiation. Thus, a drop passing along the side of the beam may not create a sufficient disturbance of the light path to result in the actual determination that a drop has fallen. The situation can occur particularly when the drip chamber hangs at an angle as when a patient may in effect pull on it when moving about in his bed. The problem becomes particularly difficult when the drip chamber hangs at such an angle that the drop, rather than falling, actually slides down the side of the chamber. Under these circumstances, drops will very likely escape the light beam and go totally undetected.
In an effort to avoid the nondetection of drops passing on the side of the beam of light, more recent flow detectors employ several beams of light from various emitters criss-crossing the drip chamber to separate detectors. This presumably provides more complete coverage of the drip chamber to avoid a drop escaping interrupting any one particular beam. However, a drop interrupting one light beam can very well give reflectances that detectors for other light beams may well receive. These various signals may result in the circuitry connecting to the receivers actually determining that no drop has fallen. Additionally, dead areas may exist between the various beams that would permit drops, especially flowing along the side, to again escape detection. Accordingly, the search continues for improved optical systems for flow detectors that will provide assurance that all drops will undergo detection.